This invention relates to a method for producing a viewing-screen structure; for example, for a cathode-ray tube.
In U.S. Pat. No. 3,533,719, issued Oct. 13, 1970 to Louis J. Angelucci, Jr., there is described a photographic method for producing a luminescent viewing screen for a cathode-ray tube. That method comprises coating a supporting surface with a film consisting essentially of organic polymeric binder material whose solubility is altered when it is exposed to radiant energy (photobinder) and particles of inorganic light-scattering material. The film is exposed to an image in the form of radiant energy, thereby producing regions of greater solubility and regions of lesser solubility in the film. The exposed film is developed by removing the regions of greater solubility and retaining the regions of lesser solubility. Particles of screen-structure material, such as phosphor particles, are adhered to the film regions of lesser solubility either before or after developing the film. The amount of material that remains adhered has, heretofore, usually been limited to a closely-packed monolayer of particles. This may cause variations in light output as well as low light output, as compared with a multilayer of particles. The retained film regions carrying the screen-structure material are baked at temperatures below about 500.degree.C to volatilize the organic material that is present.
The particles of light-scattering material in the film serve the function of increasing the efficiency of the exposing step, thereby shortening the exposure (time and/or intensity) required. Also, the light-scattering particles produce a more uniform exposure in the irradiated regions of the film. The light-scattering particles disclosed in the cited Angelucci patent are exemplified by dibasic calcium phosphate, milk of magnesia, magnesium silicate, and talc. All of these materials are inorganic and are not volatilized below about 500.degree.C. As a result, a residue of the light-scattering particles remains after the structure has been baked. Such residue has the effect of reducing the efficiency or degrading the performance of the viewing screen. Also, some of these materials dissociate in water and have an adverse effect on the physical properties of the films produced, and on the method in general.